The invention relates generally to an elevator for an earth moving scraper and more particularly to improved means for driving the elevator chains and the soil-propelling flights which are mounted on the chains.
Elevator drive systems have commonly employed an hydraulic motor having a flywheel and a speed reduction gear box. In some installations electric motors have been used. In addition, torque converters and slip couplings have sometimes been included in the drive train.
Earth moving elevators have also been mechanically powered from the prime mover or from an auxiliary engine, transmitting power through universal joints and drive shafts, plus suitable intermediate gear boxes as required, and eventually driving a main gear box at one side of the elevator.
Because of the space required for conventional elevator drive system components, the elevator flight width must be reduced, averaging, in a commercial scraper, only about 70 percent of the bowl width or about 62 percent of the scraper width. As might be expected, using an elevator of narrow width results in inefficient operation since the soil cannot be moved from the front to the back of the bowl progressively over the entire body width. Loading efficiency is further reduced since soil being conveyed up the slope tends to escape between the ends of the flights and the bowl side sheets, spilling down the slope at each side and being partially lost on the ground and partially recirculated again into the intake area of the elevator.
Moreover, the elevator is relied upon to retain the soil in the bowl during transport, and where there is a gap between the ends of the flights and the wall of the bowl an escape passage is provided resulting in leakage and scattering of dirt along the transport path.
Also a large gap between the flight ends and the wall of the bowl, particularly in the region of the blade base, results in inadequate cleaning of the bowl at time of dumping, particularly when handling clayey soils, so that "dead" material is carried on successive round trips thus reducing the material delivered in each trip.
Quite apart from distribution and retention of the soil within the bowl, a serious problem arises from the mismatch between the width of the strip of soil loosened by the blade and the elevator which is relied upon to transport the soil away from the region of the blade, resulting in failure to load the soil which is loosened at the blade ends.
Then too, there is the problem of wear and damage to the drive components. Where the elevator is of narrow width, the sprockets are inherently closer to the longitudinal center line adjacent the region of central heaping of the soil so that the sprockets and chains tend to run in the loaded material. Where the material is of an abrasive nature, wear of the moving parts may be extremely rapid. Moreover, where the chains and sprockets run in the loaded material there is serious risk that rocks and hard pieces of debris may be caught or wedged between chain and sprocket in the region of convergence to impose severe loads on the chain and drive system, resulting in sudden or incipient breakage requiring the machine to be taken out of service until a repair can be made. Other debris of a tough nature may be wound around the sprocket causing a build-up under the associated chain and imposing added resistance for the drive to overcome, to the point of stalling the elevator as well as straining the components and reducing their life expectancy.
Efforts have been made in the past to employ longer flights, notwithstanding the limitations imposed by the drive. For example, elevator motors or drive components, including gear boxes, have been extended in projecting position, cantilever fashion, beyond the overall width of the rest of the vehicle. However, this places the motor and drive components in a vulnerable position where they may be easily damaged by trees, rock banks and adjacent structures and also by other passing vehicles. Moreover, the overall width of the machine, being increased by the overhanging drive arrangement, requires increased roadway widths and door widths and increased shipping expense because of the increased cubic size of the vehicle or by the cost of disassembly in an effort to reduce such cubic size.
In lieu of mounting the motor and other drive elements in an outwardly projecting position, the drive sprockets have been moved more closely together, enabling the motor and gear box to be axially retracted and with the flight ends being extended closer to the bowl side sheets so that considerable overhand exists between the flight ends and the driving components which are adjacent to one of the sprockets. However, with the gear box and motor housing occupying an inwardly retracted position, under the overhanging flight ends, flight clearance is extremely limited so that material carried by the flights causes considerable wear to the housing and related attachments, particularly when handling the more abrasive materials. Also because of the small clearance, rocks and debris carried by the flights may be wedged between the flights and the housing, damaging these components and raising the likelihood of a jamming condition causing immediate failure requiring extensive shut-down. Moreover, moving the motor and gear box inwardly requires that the conveyor sprockets be more closely spaced, so that the chains and their sprockets must run buried in the abrasive material with correspondingly shortened life.
In still other elevator constructions the motor and gear box have been moved to a position between the chain sprockets. While this enables the sprockets and chains to be more widely spaced and reduces the degree of flight overhang, the close clearances give rise to the same problem of wear and incipient jamming.
Finally, for the purpose of avoiding overhang of the drive, designers have resorted to the expedient of offsetting the elevator toward one side of the bowl to gain space at the other side for the drive. This, as might be expected, reduces the loading efficiency and unbalances the load in the bowl with unfortunate effects upon weight distribution. Moreover, the offset results in a large space being left at one side through which leakage may occur both in loading and transport.